Since last summer, for my 1984 500SEL, the AC no longer works and I am lost on what to check. When I press the AC switch, none of the AC components engage. I checked for current at the compressor and there's none when the AC is switched on, although the switch itself lights up. All fuses are good and I believe the relay itself is good as well. The AC hasn't worked ever since I ran it for 5 hours straight on a long drive, so maybe it's a burnt wire? What should I check first and how should I approach tracing the wiring down to the problem?